Microwave survey of the conformational landscape exhibited by the propeller molecule triethyl amine

Overview & Synopsis

Conformational studies with quantum chemical methods yielded for the most stable conformer of triethyl amine a propeller-like structure belonging to the point group C3, which corresponds to an oblate top. The microwave spectrum of this conformer with 14N hyperfine splitting of all rotational transitions was assigned and molecular parameters were determined. The rotational constants were found to be A = B = 2.314873978(11) GHz, the 14N quadrupole coupling constant χcc = −5.2444(07) MHz. The observed spectrum could be reproduced within experimental accuracy. The standard deviation of a global fit with 48 rotational transitions is 1.5 kHz. The propeller-like structure seems to be energetically favorable and therefore also typical for related systems like triethyl phosphine, triisopropyl amine, tri-n-propyl amine, and tri-tert-butyl amine. Furthermore, the rotational transitions of two isotopologues, 13C2 and 13C5, could be measured in natural abundance and fitted with an excellent standard deviation. The C rotational constants could be determined to be 1.32681(96) GHz and 1.32989(18) GHz for the 13C2 and 13C5 isotopologues, respectively.